1. Field of the Invention
This invention relates to a recording power determining method of determining the optimum recording power even if an optical disc has a face deflection or an eccentricity and to an optical disc apparatus.
2. Description of the Related Art
When data is written onto an optical disc, such as CD-R or DVD-R, the optimum recording power is determined by doing test writing before final writing in order to write data with high quality.
To determine a recording power, test writing is done onto a test area set on an optical disc while changing the recording power of the laser beam sequentially. The test-written signal is reproduced, thereby measuring the asymmetry value (or signal quality).
If the optical disc has a face deflection or an eccentricity, the power of the laser beam applied to the recording tracks on the optical disc changes. Specifically, a drop in the recording power resulting from a focus shift caused by a face deflection or from a track shift due to an eccentricity makes it impossible to record the signal properly, which impairs the reliability of the determined recording power.
The technique for determining the recording power through eliminating the effects of a face deflection and an eccentricity has been disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2004-171768.
In the prior art, test recording is done while changing the recording power sequentially around the disc. After the test recording, the test-recorded signal is reproduced, determining the asymmetry value in each recording power. From the measured value, a linear or quadratic approximation characteristic of the asymmetry value in the recording power is determined. From the determined linear or quadratic approximation characteristic, a recording power to realize a specific target of the asymmetry is found. To complete the test recording on just one round of the disc, the approximation characteristic is designed to be free from the face deflection or eccentricity components when the linear or quadratic approximation characteristic is determined from the measured result. Moreover, a light beam with unrecording power to do no recording is irradiated, thereby detecting the periodic fluctuation components of the reflected light beam due to a face deflection or eccentricity of the disc. The light beam with recording power is corrected so as to cancel the components.
However, for example, when a case where a position where the effect of a face deflection of the disc is large overlaps with a position where recording is done with the optimum power is compared with a case where a position where the effect of the face deflection is small overlaps with a position where recording is done with the optimum power, there appears a difference between the determined approximation characteristics, which causes the problem of impairing the reliability of test recording.